The optical properties of carbon dioxide are well known and have particularly been used in vascular examination, particularly hepatic and cardiac vascular examination, by means of X-rays.
Until the present, the injection of carbon dioxide, preceding by a fraction of a second the taking of an X-ray, is effected by means of a conventional syringe, for example of the type comprising a piston on which one presses manually, and this adjacent the X-ray beam. The user of the syringe is thus exposed to an important dosage of X-ray.